Low dropout regulators are widely used for powering electronic circuit blocks. In applications where the power conversion efficiency is not particularly demanding, they are preferred over switching regulators for to their simplicity and ease of use.
FIG. 1 is a transistor schematic diagram of an LDO regulator 10, as known in the prior art. LDO regulator 10 includes a pair of amplifiers 12 and 14, and a pass transistor 16. Amplifier 14 together with pass transistor 16 form a fast and high current unity gain voltage follower adapted to maintain output voltage VOUT within a predefined range in response to a fast load transient. Amplifier 12 is used to form an outer feedback loop adapted to control the DC accuracy of regulator 10. In order to guarantee stable operation while satisfying output voltage accuracy requirements, system partitioning is made such that amplifier 14 has relatively low voltage gain and high bandwidth whereas amplifier 12 has a relatively high voltage gain and low bandwidth. Amplifier 12 additionally has a requirement for low input referred offset voltage as it directly impacts the accuracy of the output voltage of regulator 10. The low bandwidth, high gain and low input offset requirements are generally satisfied with specialized manufacturing processes which supports integrated capacitors and components with good matching properties, which are also expensive compared to non-specialized manufacturing processes. Additionally, the resulting amplifier 10 is usually one of the largest circuit blocks in size, compared to other blocks in the LDO.